The cracks developed in the concrete pavement due to the freezing and thawing cycle of the aggregates is called S-cracking.

Proper amount of entrained air in concrete results in (i) Better workability (ii) Better resistance to freezing and thawing (iii) Lesser workability (iv) Less resistance to freezing and thawing

A

(i) and (ii)

B

(i) and (iv)

C

(ii) and (iii)

D

(iii) and (iv)

Proper amount of entrained air in concrete results in
(i) Better workability
(ii) Better resistance to freezing and thawing
(iii) Lesser workability
(iv) Less resistance to freezing and thawing

A

(i) and (ii)

B

(i) and (iv)

C

(ii) and (iii)

D

(iii) and (iv)

Consider the following statements: 1) workability of concrete increases with the increase in the proportion of water content 2) Concrete having small-sized aggregates is more workable than that containing large-sized aggregate 3) For the same quantity of water, rounded aggregates produce a more workable concrete mix as compared to angular and flaky aggregates 4) A concrete mix with no slump shown in the slump cone test indicates its very poor workability Which of the above statements are correct?

A

1, 2 and 3 only

B

1, 2 and 4 only

C

1, 3 and 4 only

D

2, 3 and 4 only

It is desired to freeze 10,000 loaves of bread each weighing 0.75 kg from an initial room temperature of 18°C to a final temperature of -18°C. The bread-freezing operation is to be carried out in an air-blast freezing tunnel. It is found that the fan motors are rated at a total of 80 horsepower and measurements suggest that they are operating at around 90% of their rating, under which conditions their manufacturer’s data claims a motor efficiency of 86%. If 1 ton of refrigeration is 3.52 kW, estimate the maximum refrigeration load imposed by this freezing installation assuming that fans and motors are all within the freezing tunnel insulation and the heat-loss rate from the tunnel to the ambient air has been found to be 6.3 kW. Extraction rate from freezing bread (maximum) = 104 kW

A

46 tons of refrigeration

B

40 tons of refrigeration

C

56 tons of refrigeration

D

50 tons of refrigeration

Consider the following statements: 1. A high aggregate impact value indicates strong aggregates. 2. A low aggregate crushing value indicates high crushing strength of aggregates. 3. Aggregates having elongation index values greater than 15% are generally considered suitable for pavement construction. 4. Flakiness index of aggregates should not be less than 25% for use in road construction. Which of the above statements are correct?

A

2 and 3 only

B

2 and 4 only

C

1 and 3 only

D

1 and 4 only

The following statements (S1, S2, S3) pertain to mass concreting. Which of the following statements are correct? S1: The materials preferred for mass concrete are: Portland cement with low heat of hydration, Pozzolanas, Aggregates (coarse and fine), Water, Admixture, Coolants. S2: Slump of mass concrete shall be the same or more than ordinary concrete work. S3: Concrete with a low water cement ratio, correctly consolidated and properly cured provides durability to mass concrete work.

A

S1 and S2 only

B

S2 and S3 only

C

S1 and S3 only

D

S1, S2, S3

______ admixture is used to help the pavement withstand the freezing and thawing cycle.

A

Retarders

B

Plasticisers

C

Accelerators

D

Air-entraining

Which of the following statements is/are true about the advantages of prestressed concrete structure? A. In the prestressed concrete structure, the deflection of beams is considerably reduced. B. Prestressing decreases cracks in concrete under all stages of loading. C. Prestressed concrete requires only 1/3 rd of the concrete required for R.C.C.

A

Only A

B

B and C

C

A, B and C

D

Only C

Consider the following statements for air-entrained concrete: (i) Air-entrainment reduces the water demand for a given level of workability. (ii) Use of air-entrained concrete is required in environments where cyclic freezing and thawing is expectedWhich of the following is TRUE?

A

Both (i) and (ii) are True

B

Both (i) and (ii) are False

C

(i) is True and (ii) is False

D

(i) is False and (ii) is True

If concrete is exposed to repeated freezing and thawing after the final set, the final qualities of the concrete may also be __________

A

Impair

B

Aid

C

Improve

D

Extend

The cracks developed in the concrete pavement due to the freezing and thawing cycle of the aggregates is called S-cracking.

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